This invention relates generally to a fiber optic transmission line and, more particularly, to such a line suitable for use in an optic signal transmitting cable, such as a submarine cable.
Fiber optic elements now have an attenuation low enough for them to be considered for routine signal communication in much the same manner as coaxial cables are now used. Fiber optic elements have the advantage of thousands of times more band width as well as smaller size and weight than electromechanical cables. The problem associated with incorporating optical fibers in cables is that they are very fragile and are easily abraded or broken. Recent information further indicates that the optical transmission characteristics of the fibers are seriously degraded when the fibers are subjected to even small stresses. For example, an optical glass fiber should not be strained more than 0.1%. The strain of a typical electromechanical light weight cable when lowered to the ocean floor is in the order of 0.1%. For an electromehcanical steel armored cable, the strain will be in the order of 1% because of the weight of the steel armor. Obviously, therefore, an optical fiber in its normal form cannot be incorporated in a conventional electromechanical-type cable without the transmission characteristics of the fiber being subjected to degradation. Also, since optical fibers are extremely fragile and are easily abraded or broken, they cannot be processed in standard cable manufacturing equipment in their normal form.
What is desired, therefore, and constitutes one purpose of the present invention is to provide a fiber optic transmission line subassembly which has sufficient strength and protection for processing on standard cable manufacturing equipment. Another purpose of the invention is to provide a fiber optic transmission line that is designed so that it will significantly limit, if not eliminate, stress and abrasion to the optical fibers therein even though the line is contained in a cable that is operated in a standard manner and therefore subject to substantial stresses.